This invention relates to anode electrodes and, in particular, to nickel anode electrodes and to methods for making same.
Nickel anode electrodes for molten carbonate fuel cells have suffered in the past from creep and structural stability effects as well as from lack of resistance to sintering during prolonged fuel cell use. The presence of the latter effects, in turn, leads to other undesirable consequences. Thus, the anode structure is found to exhibit changes in its pore spectrum and increased contact resistance with attendant loss of electrical contact. Additionally, the anode structure is found to manifest electrolyte migration due to overlapping pore formation. This, in turn, causes electrolyte creep and wetting of the catalyst.
A variety of attempts have been made to reduce electrode creepage and increase sintering resistance in an effort to reduce or eliminate the above effects. In one such attempt, lithium aluminate has been physically and chemically impregnated into the nickel electrode structure. This technique, however, has not provided satisfactory results; since the ceramic particles incorporated into the structure stay at the metallic surface only and do not act as sites for inhibiting dislocation movements.
Another attempt at reducing electrode creepage and increasing sintering resistance has centered around the use of nickel chromium alloy to provide Cr.sub.2 O.sub.3 dispersoids in the electrode structure. Electrodes made in this way have evidenced some short term improvement, but over the long term, the alloy evidences accelerated creep and physical changes due to an unstable internal structure formed by the Cr.sub.2 O.sub.3 dispersoids in the nickel metal matrix. While higher chromium levels have resulted in satisfactory creep strength, the formation of an outer growing Cr.sub.2 O.sub.3 layer at the expense of the internal oxide dispersoids causes electrolyte wetting and preferential loss of oxides near the gas/metal surface.
Another attempt at reducing creepage and increasing sintering resistance of the anode electrode has been to use nickel aluminum alloys to form an electrode structure stabilized by Al.sub.2 O.sub.3 dispersoids. Work in this direction has, however, been very limited due to the difficulties in initial sintering of the nickel aluminum powders.
Researchers have also used metal coated ceramic particles for anode fabrication. The sintering behavior and creep resistance of such structures, however, has not been reported.
Anode structures prepared by the prior techniques have thus not proven satisfactory for one reason or another. It is therefore an object of the present invention to provide a nickel anode structure which evidences less creepage, improved structural stability and increased sintering resistance during use.